When practice does not make perfect: Well-practiced handwriting interferes with the consolidation phase gains in learning a movement sequence

Practice on a novel sequence of movements can lead to two expressions of procedural memory consolidation: delayed performance gains evolving hours after training, and a decrease in the susceptibility of the training-related gains to interference by subsequent experience. It has been assumed that behavioral interference occurs only if a critical overlap between the representations of the two tasks exists, and that such overlap is more likely when the two tasks are novel, competing for general resources for their execution. We investigated whether the delayed gains in the simple finger-opposition sequence (FOS) learning task are more prone to interference by well practiced than by less practiced complex hand movements. Participants were trained on the FOS task in a baseline (no interference) and an interference training condition. In the Interference condition, after FOS practice, participants wrote Hebrew common words in Hebrew (native script) or a Latin script (Heblatin). Native script writing but not the less practiced Heblatin, interfered with FOS learning, with significantly reduced delayed gains. Our results show that interference can occur even when two tasks share little or no kinematic or dynamic features and indicate that the representation of complex but well-practiced movement sequences may overlap with the representation of simpler ones. This result is in line with the notion that well-practiced complex movement sequences come to be represented as simpler ones in long-term motor memory.